1. Field of the Invention
The present invention relates generally to nut-and-bolt-type fasteners, and more particularly to a lock washer having an engaging cam surface disposed on a drive head, and an opposite frictional surface defined by an enlarged annular flange.
2. Description of the Prior Art
Various problems and difficulties are encountered in providing suitable lock washers of the cam-action type that will allow for simple means to unfasten associated fastening devices. When a known lock washer is installed and tightened with the cam face of the washer engaging under the head of a cam screw, the friction between the frictional surface of the washer and the joint material will prevent the washer from turning, if the cam screw is forced to turn in the loosening direction by vibrational forces or intentionally by the use of a wrench. Accordingly, the rise of the washer cams together with the cam screw is greater than the rise of the threads on the screw shaft. Thus, the cam is liable to turn in the loosening direction by vibrational forces, causing it to slide up the cam surfaces of the interacting washer, of the cam head of the screw or bolt. This cam movement induces a wedging action that jams the nut of the screw or bolt tightly between the threads on one side and the joint via the washer o the other side. Hence, when the cam screw is loosened by a wrench, the cams will override the tops of one another, which causes the bolt to become elongated. Such stretching of the bolt can also permanently damage it, if it is stretched beyond its elastic limit into the plastic region. If the fastener is repeatedly disassembled and reassembled under the cam-overriding effect, it will eventually reach its breaking point and result in a fastener failure. The risk of fastener failures caused by repeated loosening by cam-overriding severely limits the employment of wedge-action lock washers, particularly for cap-screw applications, which often involves the use of short clamp lengths.
As an example of the known art, there is disclosed in U.S. Pat. No. 3,417,802 to Oldenkott a captive lock-washer assembly which comprises a lock washer having a plurality of flat sides, and a cam surface formed on one side and a teeth-engaging surface on the opposite side. The body is designed so that the washer is extremely thin which entails the use of a minimum amount of metal in the fabrication process.